To properly mount the Hamax Observer front-position child bike seat to a threadless headset handlebar stem (or a stem with less than 2 in clearance), you will need this A-head Bracket. This bracket option requires only 1/2 in of clearance on the stem and allows easy installation of the Observer seat. Installation of the A-Head Bracket requires removal/replacement of the handlebars by a trained bike technician. At this time, the optional Windshield accessory does not fit onto this type of mounting Bracket (it does fit on the front of the Standard Mount bracket option that comes with the Observer). Acquiring a second bracket allows you to easily transfer the seat between bikes for a multi-user household!